CVE-2015-3273 in Moodle
Summary
by MITRE
mod/forum/post.php in Moodle 2.9.x before 2.9.1 does not consider the mod/forum:canposttomygroups capability before authorizing "Post a copy to all groups" actions, which allows remote authenticated users to bypass intended access restrictions by leveraging per-group authorization.
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Analysis
by VulDB Data Team • 05/31/2022
The vulnerability described in CVE-2015-3273 affects Moodle version 2.9.x before 2.9.1 and specifically targets the mod/forum/post.php component. This security flaw represents a critical authorization bypass issue that undermines the intended access control mechanisms within Moodle's forum module. The vulnerability occurs when users attempt to post content to multiple groups, where the system should verify appropriate permissions before allowing such actions. The flaw stems from the absence of proper capability checks that would normally validate whether a user possesses the necessary permissions to post to all groups within a forum context.
The technical implementation of this vulnerability demonstrates a failure in the capability-based access control system that Moodle employs to manage user permissions. When a user attempts to "Post a copy to all groups" functionality, the system should verify that the user holds the mod/forum:canposttomygroups capability before authorizing the action. However, this verification step is missing or improperly implemented in the affected versions, allowing authenticated users to circumvent the intended authorization boundaries. This capability-based access control failure creates a path for users to post content to groups where they would normally not have permission to do so, effectively bypassing the group-based permission model that Moodle implements.
The operational impact of this vulnerability extends beyond simple unauthorized posting, as it fundamentally compromises the integrity of Moodle's group-based access control system. An authenticated user who does not possess the appropriate permissions for specific groups can now post content to those groups, potentially leading to information disclosure, unauthorized communication, or disruption of educational activities. This vulnerability particularly affects institutions that rely heavily on group-based learning environments where content access is strictly controlled. The implications become more severe in educational settings where instructors need to maintain control over group discussions and where unauthorized posting could disrupt learning processes or expose sensitive information.
This vulnerability aligns with CWE-284, which describes improper access control issues in software systems, and represents a classic example of insufficient authorization checks in web applications. The flaw demonstrates how capability-based access control systems can be undermined when proper validation checks are omitted from critical functions. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation and defense evasion techniques, as it allows attackers to gain unauthorized access to group resources without detection. Organizations using Moodle should prioritize immediate patching to address this vulnerability, as it represents a significant risk to the security and integrity of their learning management systems. The remediation process requires updating to Moodle version 2.9.1 or later, which includes the necessary capability checks that prevent unauthorized group posting actions. Additionally, administrators should review and audit existing group permissions to ensure that no unauthorized posting has occurred, and consider implementing additional monitoring mechanisms to detect suspicious activities in forum modules.